Double hermetic package for fiber optic cross connect

ABSTRACT

The present invention provides a double fiber optic cross connect (OXC) package. The double package includes a substrate with a first surface and a second surface; a micromirror array coupled to the second surface of the substrate; a first cap optically coupled to the micromirror array; and a second cap optically coupled to the micromirror array. The first cap, along with a substrate populated with a micromirror array and a set of sidewalls, form a volume which is preferably hermetically sealed. This volume is further packaged by the second cap with another set of sidewalls. With the first cap, only a short distance is used in redirecting the light. This short distance is uniform for each micromirror in the switch. The major portion of the beam is thus available for scanning. With the second cap, the light beam is folded during the switching operation, resulting in a smaller switch package. By folding the light in the switch architecture, the size of the switch package is reduced. Using the substrate in combination with a modular approach to substrate population allows for a single substrate switch with a higher device yield and scalability. Integrated circuits may be placed on the same substrate as the micromirrors, and the complexity of the assembly process is reduced.

FIELD OF THE INVENTION

The present invention relates to fiber optic cross connects, and moreparticularly to the packaging for fiber optic cross connects.

BACKGROUND OF THE INVENTION

The use of optical cross connect (OXC) switching systems are well knownin the art for directing a light beam from one optical port in anoptical transmission system to another optical port. In a typical OXC, aplurality of input optical fibers, or ports, carry light beams into theOXC. The OXC then directs, or switches, the light beams to theirrespective plurality of output ports. Many conventional OXCs perform theswitching utilizing numicromirrors, which are micro-machined onto asubstrate. The micromirrors are used to reflect a light beam from aninput port to a particular output port. In this specification, the words“input” and “output” are used to indicate a direction of travel for alight beam into and out of, respectively, a switch. In reality, theinput and output ports can be used simultaneously for input and output,as is the case in bi-directional data transfer.

High port count switches utilizing micromirrors are of high demand inthe industry. Such switches require a tight packing density of themicromirrors onto the substrate. Some conventional switches use adigital switching matrix for N input and N output ports with an N×Narray of micromirrors. This requires a total of N² number ofmicromirrors. However, this architecture becomes impractical for switchport counts greater than a few hundred.

Some conventional switches use an analog switching matrix for N inputand N output ports. This requires 2*N micromirrors. In thisconfiguration, two separate substrates, or one very large substrate, arenecessary to accommodate port counts greater than a few hundred.However, the use of more than one substrate is cumbersome as they needto be aligned to each other within the package of the switch. This addscomplexity to the assembly of the package and increases package size.Also, with a hundred or more micromirrors on a single substrate, or onehalf of a two-substrate OXC, device yield is compromised due to thelarge number of possible failure points. Additionally, the opticalcomponents of the OXC are typically hermetically sealed. Such hermeticsealing of the optical components requires additional complex steps inthe manufacturing process, such as metallization of the fibers oroptical component attached to the fibers.

For many conventional switches, each micromirror also utilizes differentamounts of the Rayleigh Length for redirecting light beams. The RayleighLength is a maximum distance that a beam of light can be keptcollimated. The Rayleigh Length depends on the wavelength and minimumdiameter “waist” of the beam. The Rayleigh Length is well known in theart and will not be described in detail here. This “redirection length”,as used in this specification, is typically the length from a collimatorto an input mirror and from an output mirror to another collimator. Theremaining portion of the Rayleigh Length, i.e., the length from theinput mirror to the output mirror, is available for scanning. Becausethe redirection length varies from micromirror to micromirror, thescanning length also varies. This requires the switch to be designed sothat the longest redirection length is assumed for all micromirrors inthe switch in order to minimize optical loss and crosstalk. However, inassuming the longest redirection length for all micromirrors, thedensity of micromirrors is compromised.

Accordingly, there exists a need for an improved OXC package whichreduces the size of the package while still allowing a high port count.The improved package should also minimize optical loss and crosstalk andalso allow a tight packing density of micromirrors. The presentinvention addresses such a need.

SUMMARY OF THE INVENTION

The present invention provides a double fiber optic cross connect (OXC)package. The double package includes a substrate with a first surfaceand a second surface; a micromirror array coupled to the second surfaceof the substrate; a first cap optically coupled to the micromirrorarray; and a second cap optically coupled to the micromirror array. Thefirst cap, along with a substrate populated with a micromirror array anda set of sidewalls, form a volume which is preferably hermeticallysealed. This volume is further packaged by the second cap with anotherset of sidewalls. With the first cap, only a short distance is used inredirecting the light. This short distance is uniform for eachmicromirror in the switch. The major portion of the beam is thusavailable for scanning. With the second cap, the light beam is foldedduring the switching operation, resulting in a smaller switch package.By folding the light in the switch architecture, the size of the switchpackage is reduced. Using the substrate in combination with a modularapproach to substrate population allows for a single substrate switchwith a higher device yield and scalability. Integrated circuits may beplaced on the same substrate as the micromirrors, and the complexity ofthe assembly process is reduced.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a side view of a preferred embodiment of a switcharchitecture with a double package in accordance with the presentinvention.

FIG. 2 illustrates a side view of a substrate in the switch architecturewith a double package in accordance with the present invention.

FIGS. 3A and 3B illustrate a top view and a side view, respectively, ofa method of substrate population for the switch architecture with adouble package in accordance with the present invention.

FIGS. 4A and 4B illustrate a top view and a side view, respectively, ofan array of photodetectors on the short cap in accordance with thepresent invention.

FIG. 5 illustrates an alternative switch architecture with a doublepackage in accordance with the present invention.

DETAILED DESCRIPTION

The present invention provides an improved optical cross connect (OXC)package which reduces the size of the package while still allowing ahigh port count. The following description is presented to enable one ofordinary skill in the art to make and use the invention and is providedin the context of a patent application and its requirements. Variousmodifications to the preferred embodiment will be readily apparent tothose skilled in the art and the generic principles herein may beapplied to other embodiments. Thus, the present invention is notintended to be limited to the embodiment shown but is to be accorded thewidest scope consistent with the principles and features describedherein.

The improved OXC package in accordance with the present inventionprovides a double package comprising a first cap with reflectingsurfaces and a second cap. The first cap, along with a substratepopulated with a micromirror array and a set of sidewalls, form a volumewhich is preferably hermetically sealed. This volume is further packagedby the second cap with another set of sidewalls. With the first cap,only a short distance is used in redirecting the light. This shortdistance is uniform for each micromirror on the switch. The majorportion of the beam is thus available for scanning. With the second cap,the light beam is folded during the switching operation, resulting in asmaller switch package.

To more particularly describe the features of the present invention,please refer to FIGS. 1 through 5 in conjunction with the discussionbelow.

FIG. 1 illustrates a side view of a preferred embodiment of a switcharchitecture with a double package in accordance with the presentinvention. This architecture comprises a substrate 100 and preferably atwo dimensional array of micromirrors 204 on the substrate surface 104.In the preferred embodiment, the micromirrors 204 are divided into aplurality of input mirrors 304 and a plurality of output mirrors 306.The substrate 100 is attached to the sidewalls 308. The sidewalls 308are then attached to a first cap 310.

FIG. 2 illustrates a side view of the substrate in the switcharchitecture with a double package in accordance with the presentinvention. The preferred embodiment of the substrate 100 is a rigid andtransparent single or multi-layered planar slab with a first 102 andsecond 104 parallel surfaces. The substrate 100 may be composed of anymaterial which allows the substrate 100 to be optically transparent tothe wavelengths of interest. As illustrated, light may enter thesubstrate 100 from the first surface 102 via a plurality of opticalfibers 106 attached to a fiber housing 108. The housing 108 can includea single holder or more than one holder containing independently alignedoptical fibers 106. The substrate 100 is preferably coated on the first102 and second 104 surfaces with conventional anti-reflective coatingsto avoid reflections back to the fiber housing 106. Also, the substrate100 can be coated with a conductive layer to prevent charge build up onthe substrate 100. The light then traverses through the substrate 100and exits from the second surface 104. Chips containing the micromirrors204 and other reflective elements populate the second surface 104 of thesubstrate 100. The chips may comprise either static mirrors, activemirrors, or a combination of static and active mirrors. In the preferredembodiment, the housing 108 may contain embedded optical collimators110. Each collimator 110 is placed at a specific angle, θ₁-θ₃. Thehousing 108 may be composed of any appropriate material. Various methodsof collimation and/or redirection may be used, such as with lends,diffractive components collimator, and other appropriate componentscollimator.

Although the preferred embodiment of the substrate is described above asbeing a transparent slab, one of ordinary skill in the art willunderstand that any substrate which allows light beams to traversethrough it is within the spirit and scope of the present invention. Forexample, the substrate may be a silicon wafer with holes etched all theway through to allow light beams to pass through it. Alternatively, thesubstrate may be a double-side polished silicon wafer on which themicromirrors are fabricated. In this case, appropriate anti-reflectingcoatings are applied to both surfaces of the substrate.

The substrate is further described in co-pending US patent applicationentitled “Fiber Optic Cross Connect with Transparent Substrate”, Ser.No. 09/549,789, filed on Apr. 14, 2000 Applicants hereby incorporatethis patent application by reference.

Returning to FIG. 1, the substrate 100, sidewalls 308, and the first cap310 together provide a volume. This volume is preferably hermeticallysealed. If the substrate 100 is hermetically sealed, then the fibers 106can be dust and moisture proof sealed without the need to hermeticallyseal them. This provides ease in assembly of the switch with the fibers106. If the volume is hermetically sealed, since this volume is small,it is possible to safely pressurize the volume prior to sealing. A highpressure within the volume will assist in damping the ringing of themicromirrors 204, as well as allow better heat dissipation due togreater thermal conductivity.

Within this volume, chips with micromirrors 204, conductive traces, andintegrated circuits populate the surface 104 or 102 of the substrate100. The population of the second surface 104 of the substrate 100 withmicromirrors 204 may be accomplished in a variety of ways. One way ofpopulating the second surface 104 is illustrated in FIGS. 3A and 3B.FIGS. 3A and 3B illustrate a top view and a side view, respectively, ofa method of substrate population for a switch architecture with a doublepackage in accordance with the present invention. A plurality of chips202, each containing at least one micromirror 204, are placed onto thesecond surface 104 of the substrate 100. In the preferred embodiment,the chips 202 are placed and configured on the substrate 100 in strips206, with a plurality of chips on each strip. The strips 206 may then belocated sparsely on the substrate 100. Because each group ofmicromirrors 204 is on a separate chip 202, the chips 202 may beseparately selected to be placed onto the substrate 100, providingflexibility in how the substrate is populated. Chips with defectivemicromirrors 204 may be discovered prior to configuration of the chips202 so that only good chips 202 are used in the micromirror array 204.This improves the yield of the chips switch. Also, if any of themicromirrors 204 become damaged after placement, its chip may bereplaced without disturbing the other chips. The entire micromirrorarray 204 need not be discarded.

Although the present invention is described as fabricating the chips instrips, one of ordinary skill in the art will understand that any chipcluster size, including single chip size, may be used without departingfrom the spirit and scope of the present invention.

The second surface 104 may also comprise conductive traces 208 for thetransfer of electrical signals from wire bonds 210, or other electricalconnections to external conductors, to the micromirror array 204 for thepurpose of controlling the micromirrors 204 or signal sensing. Thesubstrate 100 also allows inclusion of integrated circuits 212 close tothe micromirrors 204 for control and positioning of the micromirrors204. This eliminates the need for a separate chip for the integratedcircuits, as is required with conventional switches. Also, with theconductive traces 208 and the integrated circuits 212 so close to themicromirror array 204, shunt capacitance and noise coupling between themare reduced. Each integrated circuit 212 may be placed at the samedistance from their respective micromirror, either on the micromirrorchips 202 and/or on the substrate 100. This allows even lower shuntcapacitance and noise coupling, providing clearer signals.

The housing 108 (FIG. 2) is aligned such that all components, such asintegrated circuits 212 and conductive traces 208, are absent from thepath of light beams from the fibers 106. By using this modular approachto substrate population, high port count switches may be formed. Thechips 202, micromirrors 204, and integrated circuits 212 may all betested prior to final assembly, so that the switch has a lower failurerate.

This modular approach to substrate population is further described inco-pending US patent application, entitled “Modular Approach toSubstrate Population For Fiber Optic Cross Connect”, Ser. No. 09/54,799,filed on Apr. 14, 2000. Applicant hereby incorporates this patentapplication by reference.

Returning to FIG. 1, the first cap 310 is a slab with its largersurfaces parallel to the substrate surface 104. Above the first cap 310is a second cap 316. Sidewalls 322 attach the second cap 316 either tothe substrate 100 or the first cap 310. Preferably, the sidewalls 322are hermetically attached to the second cap 316 and the substrate 100.In final assembly, a double packaging architecture is provided. Then,the fiber optic array 106 is aligned, and the housing 108 is attached tothe substrate 100.

In performing a switching operation, a light beam 301 enters the switch300 from the substrate surface 102 via an input optical fiber 106attached to the housing 108. A light beam 301 traverses through thesubstrate 100 and exits from the surface 104 at a portion absent ofcomponent, such as the integrated circuits 212 and conductive traces208. After the light beam 301 exits the substrate surface 104, areflecting area 312 on the first cap 310 directs the beam 301 onto aspecific input mirror 314. The reflecting area 312 may be on either ofthe surfaces of the first cap 310 parallel to the substrate surface 104.

The reflecting area 312 may be a flat mirror or a curved mirror. Ifcurved, it is preferably spherical, which may substitute for thecollimators 110 (FIG. 2) in the housing 108. The collimated portion ofthe beam 301 then begins at this mirror on the first cap 310. Thereflecting area 312 can also be fabricated into an appropriatediffractive lens, to accomplish the same objective as the curved mirror.After reflection from the input micromirror 314, the light beam 301 isdirected through the first cap 310 towards the second cap 316. The areathrough which the beam 301 penetrates the first cap 310 is transparent.The bottom or top surface of the second cap 316 is partially or whollyreflective. A reflection occurs at the second cap 316 which directs thelight beam 301 to the desired output mirror 318. Importantly, thereflection from the input mirror 314, to the second cap 316, and then tothe output mirror 318, folds the beam 301 so that the distance betweenswitch components 314 & 318, and thus the height of the package 300, isdrastically reduced.

The output mirror 318 directs the light beam 301 towards anotherreflecting area 320 on the short cap 310. The reflecting area 320functions in a similar manner as reflecting area 312. The reflectingarea 320 directs the beam 301 through the substrate 100 from the surface104. The beam 301 is refocused by a collimator 110 (FIG. 2) in thehousing 108 and directed to a specific output fiber 106. In this manner,a light beam from any input fiber can be directed to any output fiber.

The use of the first cap 310 allows for only a short distance to be usedin redirecting the light 301 from the collimator 110 onto the inputmirror 314, and from the output mirror 318 back to the collimator 110.The major portion of the collimated beam, i.e., from the input mirror314 to the second cap 316 and then to the output mirror 318, is thusavailable for scanning. Preferably, this portion is the Rayleigh lengthof the beam, minus twice the redirection length with the micromirrors204 optimized for this length. The “waist” of the beam then correspondsto the reflecting location on the second cap 316. It is important tolimit the scanned portion of the beam to this length because diffractionof the light beam beyond the Rayleigh Length produces increased loss andcrosstalk. The Rayleigh Length is well known in the art and will not bedescribed further here. Additionally, with the substrate 100 inaccordance with the present invention, the redirection length is thesame for each micromirror 204 in the array. This allows for theoptimization of the number of ports. With the micromirrors 204 in suchclose proximity to the collimator 110, the fibers 106 and/or thecollimators 110 have greater angular alignment tolerance. Although theswitch architecture is described with the micromirrors 204 substrate100, the the physical law of reciprocity dictates that on themicromirrors 204 may also be located on the first cap 310 withoutdeparting from the spirit and scope of the present invention.

In the preferred embodiment, array of photodetectors for monitoringtraffic may also be used with the architecture which provides a uniformredirection length and folding of light beams in accordance with thepresent invention. The information received from the photodetectors canbe used to confirm the proper selection of input/output channels in thelight beams and for monitoring the data flow. Photodetectors can monitortraffic in real time while slow photodetectors can be used to confirmcorrect channel switching.

One possible location for the array of photodetectors is on the firstcap 310. FIGS. 4A and 4B illustrate a top view and a side view,respectively, of an array of photodetectors on the first cap inaccordance with the present invention. An array of photodetectors 402can be attached on the top surface 404 of the first cap 310 fordetection and interpretation of the light beam 301. As illustrated inFIG. 4B, in this case, the reflecting surface 312 in the first cap 310is on the bottom surface 406 and partially transmitting in order toallow some light 408 to proceed to the photodetector 402. The topsurface 404 (FIG. 4A) would contain conductive traces 410 to carry thephotodetector signals to the edge of the first cap 310, where it wouldbe electrically connected to the traces on the substrate 100, such aswirebonds 412 from bonding pads.

In addition to photodetector 402, triangular clusters of three or moreequally spaced photodetectors 414 can be used on either side of aphotodetector 402 to perform other monitoring or sensing functions, suchas mirror angle sensing. Assuming that the light beam 301 is travelingin the output direction, the three photodetector signals around the beam418 can be used to interpret the ‘centering’ of the beam 418. Bycombining information from the triangular clusters of photodetectors414, 416 around each beam 418, and the optical power focused into afiber, the required mirror position for maximum optical power transfercan be determined. Every possible switch configuration can be optimizedand the corresponding mirror position recorded, to be utilizedrepeatedly throughout the operating life of the switch.

FIG. 5 illustrates an alternative switch architecture with a doublepackage in accordance with the present invention. This architecture isidentical to the architecture illustrated in FIG. 1 except for theaddition of a third cap 502. An array of photodetectors 504 can beattached to the third cap 502. The third cap 502 is preferablypositioned from the second cap 316 at a distance which is approximatelythe same distance from the micromirrors 204 to the second cap 316. Inthis case, the reflecting surface 506 on the second cap 316 is partiallytransmitting to allow some light 508 to proceed to the photodetectors504. The characteristics of beams 508 at the micromirror array 204 arethe same for the light beams on the third cap 502. Photodetectors 504(single or in multiples) can be used similarly to the ones on the firstcap 310 as described above to collect mirror position information or tomonitor traffic on the optical beam.

Although the photodetectors are described as being located on the firstcap 310 or the third cap 502, one of ordinary skill in the art willunderstand that the photodetectors may be placed at other locationswithout departing from the spirit and scope of the present invention.For example, a cluster of three photodetectors can be placed on thesubstrate 100 where the light beam enters/exists the substrate 100. Foranother example, the photodetectors may be in the housing 108surrounding the collimators 110, or on the fibers 106.

A double OXC package has been disclosed. In the preferred embodiment,the double package comprises a first cap with reflecting surfaces and asecond cap. The first cap, along with a substrate populated with amicromirror array and a set of sidewalls, form a volume which ispreferably hermetically sealed. This volume is further packaged by thesecond cap with another set of sidewalls. With the first cap, only ashort distance is used in redirecting the light. This short distance isuniform for each micromirror in the switch. The major portion of thebeam is thus available for scanning. With the second cap, the light beamis folded during the switching operation, resulting in a smaller switchpackage. By folding the light in the switch architecture, the size ofthe switch package is reduced. Using the substrate in combination with amodular approach to substrate population allows for a single substrateswitch with a higher device yield and scalability. Integrated circuitsmay be placed on the same substrate as the micromirrors, and thecomplexity of the assembly process is

What is claimed is:
 1. A fiber optic cross connect (OXC), comprising: asubstrate with a first surface and a second surface; a micromirror arraycoupled to the second surface of the substrate; a first cap opticallycoupled to the micromirror array; and a second cap optically coupled tothe micromirror array.
 2. The OXC of claim 1, wherein the second cap ismore distally optically coupled to the micromirror array than the firstcap.
 3. The OXC of claim 1, wherein the second surface of the substrateis parallel to the first surface of the substrate.
 4. The OXC of claim1, wherein the substrate comprises a slab, wherein the slab istransparent to wavelengths of interest.
 5. The OXC of claim 1, whereinthe substrate comprises holes through which the light beams may travel.6. The OXC of claim 1, wherein the substrate comprises a double-sidedpolished silicon wafer.
 7. The OXC of claim 1, wherein the substratecomprises: a first anti-reflective coating on the first surface of thesubstrate; and a second anti-reflective coating on the second surface ofthe substrate.
 8. The OXC of claim 1, wherein the substrate comprises:integrated circuits on the first or the second surfaces of thesubstrate; and conductive traces on the first or the second surfaces ofthe substrate.
 9. The OXC of claim 8, wherein the integrated circuitsare in close proximity to the micromirror array.
 10. The OXC of claim 8,wherein the integrated circuits and conductive traces are absent frompaths of light beams traveling through the substrate.
 11. The OXC ofclaim 1, further comprising a plurality of photodetectors coupled to thesubstrate at a location where light beams travel in or out of thesubstrate.
 12. The OXC of claim 1, wherein the micromirror arraycomprises a plurality of static mirrors.
 13. The OXC of claim 1, whereinthe micromirror array comprises a plurality of active mirrors.
 14. TheOXC of claim 1, wherein the micromirror array comprises a plurality ofstrips, wherein each of the plurality of strips comprises a plurality ofmicromirrors of the micromirror array.
 15. The OXC of claim 1, whereinthe micromirror array comprises a plurality of input micromirrors and aplurality of output micromirrors.
 16. The OXC of claim 1, wherein themicromirror array is a two dimensional array.
 17. The OXC of claim 1,wherein the first cap is parallel to the first and second surfaces ofthe substrate.
 18. The OXC of claim 17, further comprising a first setof sidewalls coupled to the first cap and the second surface of thesubstrate.
 19. The OXC of claim 17, wherein the first cap furthercomprises: a plurality of reflecting surfaces, wherein the plurality ofreflecting surfaces reflects light beams between a plurality ofcollimators and the micromirror array.
 20. The OXC of claim 19, whereina distance traveled by the light beams between the plurality ofcollimators and the micromirror array is identical for each micromirrorin the micromirror array.
 21. The OXC of claim 19, wherein the pluralityof reflecting surfaces is coupled to a first surface of the first cap.22. The OXC of claim 21, further comprising: a plurality ofphotodetectors residing on a second surface of the first cap, whereinthe first surface of the first cap is approximately parallel to thesecond surface of the first cap.
 23. The OXC of claim 19, wherein theplurality of reflecting surfaces comprises a plurality of flat mirrors.24. The OXC of claim 19, wherein the plurality of reflecting surfacescomprises a plurality of curved mirrors.
 25. The OXC of claim 1, whereinthe second cap folds light beams during a switching operation.
 26. TheOXC of claim 1, wherein a first surface of the second cap is parallel toa second surface of the first cap.
 27. The OXC of claim 26, furthercomprising a second set of sidewalls coupled to the second cap and thesecond surface of the substrate.
 28. The OXC of claim 26, furthercomprising a second set of sidewalls coupled to the second cap and thefirst cap.
 29. The OXC of claim 1, further comprising a housing, whereinthe housing comprises: a plurality of optical fibers.
 30. The OXC ofclaim 28, further comprising a plurality of collimators opticallycoupled to the plurality of optical fibers, wherein the plurality ofcollimators is optically coupled to the first surface of the substrate.31. The OXC of claim 1, further comprising a third cap, wherein a firstsurface of the third cap is optically coupled to a second surface of thesecond cap.
 32. The OXC of claim 31, further comprising a third set ofsidewalls coupled to the third cap and the second cap.
 33. The OXC ofclaim 31, wherein a distance between the third cap and the second cap isapproximately equal to a distance between the micromirror array and thesecond cap.
 34. The OXC of claim 31, further comprising a plurality ofphotodetectors coupled to a second surface of the third cap.
 35. An OXC,comprising: a plurality of collimators; a substrate with a first surfaceand a second surface, wherein the first surface of the substrate isoptically coupled to the plurality of collimators; a micromirror arraycoupled to the second surface of the substrate; a first cap with a firstsurface and a second surface; a plurality of reflecting surfaces coupledto the first surface of the first cap, wherein the plurality ofreflecting surfaces reflects light beams between the plurality ofcollimators and the micromirror array; a first set of sidewalls coupledto the first cap and the second surface of the substrate; a second capwith a first surface and a second surface, wherein the first surface ofthe second cap is optically coupled to the micromirror array, whereinthe second cap folds the light beams during a switching operation; and asecond set of sidewalls coupled to the second cap and the second surfaceof the substrate.
 36. An OXC, comprising: a plurality of collimators; asubstrate with a first surface and a second surface, wherein the firstsurface of the substrate is optically coupled to the plurality ofcollimators; a micromirror array coupled to the second surface of thesubstrate; a first cap with a first surface and a second surface; aplurality of reflecting surfaces on the first surface of the first cap,wherein the plurality of reflecting surfaces reflects light beamsbetween the plurality of collimators and the micromirror array; aplurality of photodetectors coupled to the second surface of the firstcap; a first set of sidewalls coupled to the first cap and the secondsurface of the substrate; a second cap with a first surface and a secondsurface, wherein the first surface of the second cap is opticallycoupled to the micromirror array, wherein the second cap folds the lightbeams during a switching operation; and a second set of sidewallscoupled to the second cap and the second surface of the substrate. 37.An OXC, comprising: a plurality of collimators; a substrate with a firstsurface and a second surface, wherein the first surface of the substrateis optically coupled to the plurality of collimators; a micromirrorarray coupled to the second surface of the substrate; a first cap with afirst surface and a second surface; a plurality of reflecting surfaceson the first surface of the first cap, wherein the plurality ofreflecting surfaces reflects light beams between the plurality ofcollimators and the micromirror array; a first set of sidewalls coupledto the first cap and the second surface of the substrate; a second capwith a first surface and a second surface, wherein the first surface ofthe second cap is optically coupled to the micromirror array, whereinthe second cap folds the light beams during a switching operation; asecond set of sidewalls coupled to the second cap and the second surfaceof the substrate; a third cap with a first surface and a second surface,wherein the first surface of the third cap is optically coupled to thesecond surface of the second cap; a plurality of photodetectors coupledto the second surface of the third cap; and a third set of sidewallscoupled to the third cap and the second cap.
 38. An OXC, comprising: aplurality of collimators; a substrate with a first surface and a secondsurface, wherein the first surface of the substrate is optically coupledto the plurality of collimators; a plurality of photodetectors coupledto the substrate at a location where light beams travel in or out of thesubstrate; a micromirror array coupled to the second surface of thesubstrate; a first cap with a first surface and a second surface; aplurality of reflecting surfaces coupled to the first surface of thefirst cap, wherein the plurality of reflecting surfaces reflects lightbeams between the plurality of collimators and the micromirror array; afirst set of sidewalls coupled to the first cap and the second surfaceof the substrate; a second cap with a first surface and a secondsurface, wherein the first surface of the second cap is opticallycoupled to the micromirror array, wherein the second cap folds the lightbeams during a switching operation; and a second set of sidewallscoupled to the second cap and the second surface of the substrate.
 39. Asystem, comprising: a fiber optic transmission system; and an OXCoptically coupled to the fiber optic transmission system, the OXCcomprising: a substrate with a first surface and a second surface; amicrorrirror array coupled to the second surface of the substrate; afirst cap optically coupled to the micromirror array; and a second capoptically coupled to the micromirror array.